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Ultrasharp Single-Atom Tips Could Improve Microscopy

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EDMONTON, Alberta, July 12, 2006 -- New ultrasharp, single-atom tips created through a unique process could improve electron microscopy to a level that would make solutions possible to research problems currently just out of reach, its developers said.

Scientists from the University of Alberta (U of A), working out of the National Institute of Nanotechnology (NINT) at the university, used a unique process to make the sharpest tip ever known and opened the door to a range of possibilities, they said. They were able to coat peripheral atoms near the peak with nitrogen, making it a one-atom-thick, tough protective paint job.

Wolkow.jpg"That coating has the effect of binding the little pyramid of metal atoms, or tungsten, in place," said Robert Wolkow, a physics professor at the U of A and co-author on the research paper published in the Journal of Chemical Physics. "Such a pointy pyramid of metal atoms would normally just smudge away spontaneously. It's like a sand pile -- you know you can't make it arbitrarily pointy. If you try to pile on more sand, it flows down and makes a more blunt pile. Metal atoms will do the same thing."

These sharp tips are needed for making contact with metals or semiconductors as well as for the manipulation and examination of atoms, molecules and small particles. Ultrafine tips are demanded for future experiments where the results are directly dependent on shape of the tip, he said.

The tips made by Wolkow and the research team -- Moh'd Rezeq and Jason Pitters from NINT -- are so stable they withstand temperatures of 900 °C. They are so sharp they appear -- so far -- to serve as excellent emitters of electron beams, Wolkow said.

"The lenses in an electron microscope work more perfectly if the electron beam comes from a really small point," said Wolkow. "Since we have the smallest point source of electrons, we think we will be able to make the best electron microscopes." This is speculation, but based on pretty conventional thinking, he said.

"If this works, and it remains to be proven, it would be like taking a modest car and making it go like a race car by just changing its spark plugs. We would take a conventional electron microscope, put in one of our tips as the electron source and render the microscope instantly improved and capable of finer resolution," he said. 

Electron microscopes enable advances in diverse areas. Research problems that are just out of reach today could be made accessible by advances in electron microscopy, including studies of the little pores that form in cell walls and which are centrally important in the regulation of all life processes as well as new nanostructured materials that reduce energy consumption in vehicles.

Wolkow said he also expects their sharp tips will allow electrical characterization of extremely small objects, in turn allowing new device concepts to be discovered and tested.

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Jul 2006
A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.
A source of radiation.
An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
electronelectron microscopeemitterMetamicroscopeMicroscopyNews & FeaturesNINTsingle-atomtipsultrasharpUniversity of AlbertaWolkow

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